The development of the mammalian kidney is a very complex process, involving branching morphogenesis of the ureter and the formation of nepherons. Once the nepheron is formed, the next stage of development is for the loop of Henle and collecting duct to elongate into the renal pelvis, forming the medulla. Delineation of the spatial and temporal expression patterns of genes in kidney is essential for understanding its organogenesis and physiological function. Therefore, we proposed to analyze the expression patterns of 100 genes in the developing kidney. These genes are either novel or have not been reported to be expressed or to be functioning in the kidney. We will tag these genes with GFP to visualize the spatio-temporal expression patterns. Analyses of these mice will be enable us to: 1) determine the effect of the loss of the gene function on renal development;2) follow the fate of the homozygous mutant cells as they are now marked by GFP;and 3) determine the subcellular localization of the gene product by visualizing the GFP tag, which often time is very revealing about a gene's function